Lab talk

Jan 11, 2013

Nanoanalysis improves heart of particle accelerator

Radio frequency resonant cavities made of niobium and operated in a superconducting state are the main particle accelerating structures in modern particle accelerators. Such cavities have long suffered from a poorly understood sensitivity to surface treatments and an anomalous field dependence of wall dissipation. Now, reporting their results in the journal Superconductor Science and Technology (SuST), scientists working at Fermilab have put forward a model that could help to explain the issue.

Niobium can easily pick up hydrogen during cavity processing steps. It turns out that absorbed hydrogen segregates near the surface and upon cool-down to cavity operational temperatures of <4.4K may form normal conducting hydride nanoprecipitates. Due to proximity effects, such precipitates are also superconducting, but with altered properties and may have a lower breakdown field than the host niobium.

The model connects together experimental hints and provides both nanostructural origins and a physical mechanism of anomalous dissipation. Intensive experimental work is underway to test the proposal. If confirmed, the finding may pave the way for significant improvements in the quality factors of niobium cavities and enable cheaper and more efficient particle accelerators.

Full details can be found in the journal Superconductor Science and Technology.

About the author

Dr Alexander Romanenko is a Peoples Fellow and an Associate Scientist in the Superconducting Materials Department (SMD) within Technical Division at Fermilab. Dr Fedor Barkov is a Guest Scientist. Romanenko and Barkov’s research is funded by the DOE Early Career Award from the Office of Nuclear Physics to AR. Dr Anna Grassellino is a postdoctoral research associate in SRF Development Department. Dr Lance Cooley is head of the SMD.